1. Field of the Invention
The invention concerns a method for mode formation from at least two magnetic resonance response signals. The invention also concerns a method for mode provision for magnetic resonance imaging. Furthermore, the invention concerns of a reception unit for a magnetic resonance device with at least two local antennas that are respectively connected separately to a combination network to combine the antenna signals.
2. Description of the Prior Art
Parallel imaging techniques (Parallel Acquisition Techniques PAT) are used in magnetic resonance tomography (MR tomography) to reduce the image acquisition time. In such techniques, information regarding the locations of respective signal-receiving local antennas is used for image reconstruction. Given an arrangement of N local antennas, the image acquisition time can be maximally shortened by an acceleration factor N. The number of the local antennas used is thus always larger than or equal to the achieved acceleration factor. A reception channel of an MR imaging unit is necessary for each local antenna that is used.
If multiple local antennas are used in a parallel imaging method, and if the maximum acquisition region (Field Of View FOV) of the local antennas is scanned, a reception channel is thus necessary for each local antenna that is used, also in the case of no accelerated imaging being implemented.
An arrangement of local antennas is known from German OS 4,232,827. The arrangement formed as an array with at least three linearly polarized local coils that mutually overlap insofar as that they are geometrically decoupled, and each local coil is separately connected to a combination network in which a complex linkage is produced among the output signals respectively from three local coils, such that one MR signal is acquired that corresponds to a circular polarization.
A method for MR imaging is known from U.S. Pat. No. 4,825,162. In this method, an array of surface coils is first provided, with the surface coils positioned such that they exhibit no mutual interaction. An MR response signal, which originates from a part of the probe that is located in the acquisition region, is received by each coil. An MR image is formed from each MR response signal, and the MR images are combined with one another on a pixel-by-pixel basis in order to generate a single common MR image.
The topic of the phase-controlled group antenna is, for example, explained in “Taschenbuch der Hochfrequenztechnik”, Springerverlag 1986. In a supply network of the group antenna, phase shifters and delay elements are used that change the amplitudes and phases of the individual radiation emissions before their superimposition and influence the directional characteristics of the group antenna.
A PI/2 power element is known from European Application 03 37 194 that divides an input signal into two signal paths with equal amplitude and 90° phase shifting.